Since launching in 2009, Grindr's user base has grown to more than five million people who on average spend 90 minutes every day using the app. People seem to love the app so much that they're even willing to pay for Grindr's premium features, which make up 76% of the company's revenue.

Grindr's success has motivated a slew of competitors — some more successful than others. There's Mister for finding gay and bisexual men, OkCupid's "Locals" feature, and Tinder for finding attractive people to hook up with nearby.

But what's driving Grindr's success comes down to a few things, Woo said:

Grindr is "spontaneous and intimate," which is incredibly appealing to people.

It's much simpler and more direct than other social networking sites. When users sign up, they know exactly what to expect: flirting and hooking up. Meanwhile, a Poke on Facebook, may or may not have any romantic innuendos, depending on who sends it.

Grindr places a greater emphasis on proximity, not location. So it only shows you people who are actually physically located near you at any given time, not just people who happen to live in a certain city.

It works for more than just hookups. Two thirds of people on Grindr also use the app to find new friends nearby, or to network, according to a Grindr survey.